The present invention relates to a system for controlling an electro-magnetic clutch for automobiles, and more particularly to a system for controlling an electro-magnetic clutch which is capable of eliminating residual magnetism therein by applying inverted current to the magnetic coil, when the car speed is lower than a predetermined value.
An electro-magnetic clutch for a car comprises an annular drive member secured to the crankshaft of the engine, a magnetizing coil provided in the drive member, a driven member secured to the input shaft of the transmission spaced by a gap from the drive member, and a shift lever for changing gears in the transmission. The shift lever is provided with a switch for the magnetizing coil, which is actuated by operating the shift lever. When the shift lever is shifted to a gear engaging position, the switch is closed so that electric current flows through the magnetizing coil to magnetize the drive member. As the accelerator pedal is depressed, the clutch current passing the coil increases. The magnetic flux intensifies in the gap between the drive member and the driven member, so that the driven member is coupled to the drive member. Thus, the car can be smoothly started by suitably operating the accelerator pedal with slippage in the clutch. When the clutch current is cut off, the clutch is disconnected.
FIG. 5 shows variations of the clutch current and car speed. When the car speed is higher than a predetermined speed V.sub.1, a rated clutch current Im flows in the coil. When the car speed is lower than the speed V.sub.1, the clutch current is shut off. If the time t.sub.1 from the car speed V.sub.1 to zero is extremely short, for example, as during rapid deceleration, magnetism remains in the magnetic material of the clutch by hysteresis. The residual magnetism causes the drive member to attract the driven member, which will cause an unpleasant rattling noise in the driving system.